There are known electronic devices including a LCD touch screen which can display information and activate the various functions of the device.
For example, there are known watches including a so-called touch glass having, on the lower face thereof, capacitive electrodes acting as touch keys. These keys are activated by a conventional push-piece. The user then touches the location of a capacitive electrode to activate the desired function.
One drawback of this method is that the user must pre-activate the touch keys before selecting a function and this therefore requires an additional operation. Further, this configuration requires a key to activate a function, which consequently limits the number of functions that the device can have.
There are also known electronic devices provided with a touch screen. The touch screen includes various touch keys. To select a function, the user lightly touches or taps and then releases a touch key. The time between the application of pressure and release of pressure is measured and then compared to predefined thresholds. In fact, each predefined threshold corresponds to a function so that the duration between the application of pressure and release of pressure determines the selection of a particular function.
One drawback of this method is that it is imprecise. Indeed, the user has to press for a relatively precise period of time in order to select a function. Control of this duration is complex and therefore the user frequently selects a different function to the one required.
One solution consists in having clearly defined durations, i.e. deciding that a duration of one second selects the first function, a duration of two seconds selects a second function, a duration of four seconds selects a third function. The drawback is that selection therefore takes time which may irritate the user.